Japanese Patent Application Laid-Open No. 2011-94742 discloses a radial gap type multistage magnetic transmission mechanism the transmission gear ratio of which can be switched discontinuously. The multistage magnetic transmission mechanism is provided with: a plurality of discoid inner rotors separately disposed in the direction of the rotation axis; a plurality of annular outer rotors disposed on the outer periphery side of the inner rotors, respectively; and an annular stator disposed between the inner rotors and the outer rotors. The inner rotors are provided on the input shaft, and on the plurality of inner rotors, a different number of magnetic pole pairs are disposed in the circumferential direction. The outer rotors are provided on the output shaft, and on the plurality of outer rotors, a different number of magnetic pole pairs are disposed in the circumferential direction. The magnetic pole pairs of the plurality of outer rotors and the magnetic pole pairs of the plurality of inner rotors oppose each other. On the stator, a plurality of magnetic bodies are disposed, and the magnetic bodies are structured so as to be capable of selectively opposing one of the pairs of the opposing inner rotors and outer rotors.
The multistage magnetic transmission mechanism is capable of discontinuously switching the transmission gear ratio by moving the stator in the direction of the rotation axis.
Specifically, the stator is moved to between the inner rotor and the outer rotor constituting a first pair and the magnetic bodies are opposed to the magnet arrays, whereby one transmission portion having a first transmission gear ratio is structured. The stator is moved to between the inner rotor and the outer rotor constituting a second pair and the magnetic bodies are opposed to the magnet arrays, whereby one transmission portion having a second transmission gear ratio is structured.